Low-degree api gravity crude oil recovery process by in situ combustion



United States Patent 3,470,955 LOW-DEGREE API GRAVITY CRUDE OIL RE-COVERY PROCESS BY IN SITU COMBUSTION Fred H. Poettmann, Littleton,Colo., assignor to Marathon Oil Company, Findlay, Ohio, a corporation ofOhio No Drawing. Filed Nov. 28, 1967, Ser. No. 686,330 Int. Cl. E21b43/24 US. Cl. 166260 12 Claims ABSTRACT OF THE DISCLOSURE Recovery oflow-degree API graviy crude oil from a subterranean reservoir isfacilitated by injecting into the formation a relatively high-degree APIgravity crude oil and establishing and maintaining in situ combustionwithin the formation.

BACKGROUND OF INVENTION Recovery of crude oil from subterraneanformations by in situ combustion has proved to be very feasible. Fuelrequirements, air requirements, and character of the crude oil withinthe formation dictate the economical feasibility of such a process.United States Patent No. 2,889,881 to Trantham et a1. teaches an in situcombustion process to improve the recovery of a high-degree API gravitycrude oil by depositing within the formation a relatively low-degree APIgravity crude oil (capable of sustaining combustion) and establishing acombustion front within the formation.

Reservoirs containing a highly viscous, low-degree API gravity crudeoil, e.g. crude oil from the Belridge reservoir in California, requirefor in situ combustion as high as 25,000 to 30,000 standard cubic feetof air per barrel of crude oil recovered. This high fuel demand depositsabout three pounds of coke per cubic foot of reservoir.

Such an in situ process is economically marginal.

DESCRIPTION OF INVENTION Production from a subterranean formationcontaining a low-degree API gravity crude oil can be improved bydepositing within the formation a relatively high-degree API gravitycrude oil and then establishing combustion. Minimum fuel contentnecessary to sustain combustion should be deposited to facilitatemovement of the lowdegree API crude oil toward a production means withinthe formation. This amount of high-degree API gravity crude oil willdepend upon the well spacing and volume of reservoir to be processed.Generally, from about 2% to about 10% volume of high-degree API gravitycrude oil is required, these percents are based on the low-degree APIgravity crude oil within the reservoir. Example of such a reservoir isone containing from about 30% to about 70% oil saturation of thelow-degree API gravity crude oil.

The terms low-degree API gravity crude oil and highdegrce API gravitycrude are relative, i.e. the high-degree API gravity crude should have ahigher degree API gravity. Low-degree API gravities within the range offrom about 8 to about 20 are especially useful with this invention.Examples of useful high-degree API gravity crudes include from about 25to about Injection of the high-degree API gravity crude oil misciblydisplaces the low-degree API gravity crude oil away from the well bore.During the displacement, the low-degree API gravity crude oil is removedfrom the sand grains. Thus, sand grains are cleaned of the lowdegree APIgravity crude as the front of the high-degree API gravity crude oilprogresses through the formation.

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An adverse mobility ratio between the crudes can exist when theviscosity difference between the high-degree API gravity crude oil andthe low-degree API gravity crude oil is large. Such adversity does notexist when the difference is relatively small. In any case, theadversity is not as great as when natural gas or LPG (liquefiedpetroleum gas) is used in an in situ process.

When the mobility ratio between the lowand highdegree API gravity crudeoils is such to cause operational difliculties, from about 1% to about20% and preferably 2% to about 10% formation pore volume of a mobilitybuffer can be injected previous to the high-degree API gravity crudeoil. The mobility buffer can have a mobility between that of the crudeoil within the formation and the high-degree API gravity crude oil to beinjected. Preferably, it can have graded mobilities from a low at thelow-degree API gravity crude oil to a high at the front portion of thehigh-degree API gravity crude oil. Preferably, 5% up to of the mobilitybuffer has mobilities graded with distance by a semi-logarithmicstraightline function.

The mobility buffer can be any liquid which is moveable within theformation. It is preferred that it be compatible with both the lowandhigh-degree API gravity crude oils and that it not be substantially 100%Water. Examples of mobility buffers are miscible solutions of alcohols,oilexternal emulsions and waterand oil-external micellar solutions.Preferably, the mobility buffer is an oil-external micellar solution.Examples of micellar solutions can be found in United States Patent No.3,254,714 to Gogarty et al.; 3,275,075 to Gogarty et al.; 3,301,325 toGogarty et al., and 3,330,343 to Tosch et al.

The mobility buffer can serve to change the wettability of the formationsand. That is from a low-degree API gravity crude oil wet sand to ahigh-degree API gravity wet sand. Purpose of the change in wettabilityis to coat the sands with a lower fuel content crude oil, thus reducingthe potential coke depositing characteristics of the formationsandsdesirably to 0.5-1 pound of coke per cubic foot of reservoir.Micellar solutions are especially useful for changing the wettability.

After the high-degree API gravity crude oil is deposited within theformation, a combustion supporting material is deposited in the wellbore and combustion is initiated. Thereafter, the combustion supportingmaterial is continuously injected into the well bore to sustaincombustion. The combustion zone of the high-degree API gravity crude oiland combustion supporting material should be sufiicient to advanceitself toward a production means Within the formation to facilitate theflow of low-degree API gravity crude oil towards a production well.

The combustion supporting material is an oxygen containing solid, liquidor gas (preferably air). Also, the material can be preheated beforeinjection into the well bore. For example, the air can be preheated upto a temperature such that when it comes in contact with the high-degreeAPI gravity crude oil deposited within the formation, combustion iseffected.

The deposited oil in the formation can be ignited by any means known inthe art. For example, a squib, incendiary shell, a gas heater, anelectrical igniter, a chemical reaction can be used to obtain combustiontemperature. Also, the oxygen-containing material can be heated tocombustion supporting temperature and pumped down into the formation toignite the deposited oilfor example, preheated air is sufiicient if uponcontact with the crude oil in the formation the temperature of themixture is around 500-700 F.

Equivalents obvious to those skilled in the art are considered to beincorporated within the scope of this invention.

What is claimed is:

1. A process of recovering crude oil by in situ combustion from asubterranean formation containing a lowdegree API gravity crude oil,comprising -(1) injecting from about 1% up to about 20% formation porevolume of a micellar solution into the formation,

(2) injecting from about 2% up to about of a relatively high-degree APIgravity crude oil into the formation, the percents based on volume oflowdegree API gravity crude oil within the formation,

(3) injecting suflicient air to support combustion of the high-degreeAPI crude oil, and

(4) establishing and maintaining a combustion front within the formationto facilitate movement of the low-degree API gravity crude oil toward aproduction well within the formation.

2. The process of claim 1 wherein the low-degree API gravity crude oilhas a gravity of from about 8 to about 3. The process of claim 1 whereinthe micellar solution is characterized as having a mobility between thatof the low-degree API gravity crude oil and the high-degree API gravitycrude oil.

4. The process of claim 3 wherein from about 5% up to about 100% of themicellar solution is characterized as having mobilities gradedincreasingly with distance from front to rear by a semi-logarithmicstraightline function.

5. The process of claim 1 wherein the high-degree API gravity crude oilhas a gravity from about to about 6. A process for recovering crude oilby in situ combustion from a subterranean formation containing alowdegree API gravity crude oil, comprising:

(1) injecting a mobility buffer into the formation,

(2) injecting into the formation an amount of a relatively high-degreeAPI gravity crude to supply sufficient heat to facilitate movement ofthe low-degree API gravity crude oil in the formation,

(3) injecting sufiicient oxygen-containing material to supportcombustion of the high-degree API gravity crude oil, and

(4) establishing and maintaining a combustion front in the formation tofacilitate movement of the low degree API gravity crude oil toward aproduction well within the formation.

7. The process of claim 6 wherein the mobility buffer has a mobilitybetween that of the low-degree API gravity crude oil and that of thehigh-degree API gravity crude oil.

8. The process of claim 6 wherein the mobility buffer is a micellarsolution.

9. A process of recovering crude oil by in situ combustion from asubterranean formation containing a lowdegree API crude oil, comprising,

(1) injecting from about 1% to about 20% formation pore volume ofmicellar solution into the formation,

(2) injecting relatively high-degree API gravity crude oil into theformation to supply sufiicient heat to facilitate movement of low-degreeAPI gravity crude oil within the formation,

(3) injecting sufiicient oxygen-containing material to supportcombustion of the high-degree API gravity crude oil, and

(4) establishing and maintaining a combustion front in the formation tofacilitate movement of the low-degree API gravity crude oil toward aproduction well in the formation.

10. The process of claim 9 wherein the micellar solution ischaracterized as having a mobility between that of the low-degree APIgravity crude oil and that of the high degree API gravity crude oil.

11. The process of claim 9 wherein from about 2% to about 10% of therelatively high-degree API gravity crude oil is injected into theformation, the percents based on volume of the low-degree API gravitycrude oil within the formation.

12. The process of claim 9 wherein the low-degree API gravity crude oilhas an average gravity of from about 8 to about 20.

References Cited UNITED STATES PATENTS 2,670,047 2/1954 Mayes et a].166-11 3.026937 3/1962 Simm 16611X 3,233,671 2/1966 Chatenever 166-113,263,750 8/1966 Hardy l66l1 STEPHEN J. NOVOSAD, Primary Examiner U.S.Cl. X.R. 166272

